There is known a liquid jet recording method for conducting recording by discharging a liquid recording medium such as ink through discharging outlets utilizing thermal energy to sputter said liquid recording medium whereby said liquid recording medium is deposited on a recording member such as papers, plastic sheets, fabrics, or the like. The liquid jet recording method is of a so-called non-impact recording method, and it has various advantages in that the noise at the recording can be reduced to a negligible order, there is not a particular restriction for the recording member used, and color recording can be relatively easily attained. And as for the apparatus, that is, the liquid jet recording apparatus, for practicing the above liquid jet recording method, there are advantages in that the structure thereof can be relatively simplified, liquid discharging nozzles can be arranged at a high density, and a high speed recording can be relatively easily attained. In view of this, the liquid jet recording method has recently received he public attention, and various studies have been made thereon. Incidentally, a number of liquid jet recording apparatus have been put on the market.
Shown in FIG. 5(A) is a schematic cross-eyed view illustrating the principal part of an example of a recording head used in such liquid jet recording apparatus. FIG. 5(B) is a schematic cross-sectional view taken along the liquid pathway and at the face perpendicular to the substrate of the recording head shown in FIG. 5(A).
As apparent from FIG. 5(A) and FIG. 5(B), the recording head is provided with a substrate 8 for liquid jet recording head comprising a plurality of discharging outlets 7 each serving to discharge a liquid recording medium such as ink, liquid pathways 6 each corresponding one of the discharging outlets 7, a liquid chamber 10 serving to supply a liquid recording medium to each of the liquid pathways, heat generating resistors 2a each serving to supply thermal energy to the liquid recording medium, and wirings 3a, 3b for applying an electric signal to the heat generating resistors 2a.
The substrate for liquid jet recording head 8 is of the configuration shown in FIG. 5(B) wherein a heat generating resistor layer 2 is disposed on a base member 1, a wiring layer 3 constituted by a material having a good electroconductivity is laminated on said heat generating resistor layer 2, and a portion 2a of the heat generation resistor layer where the wiring layer 3 is not disposed functions as a heat generating resistor.
In this configuration, when an electric signal is applied to the heat generating resistor 2a through the wirings 3a, 3b the heat generating resistor 2a is energized. The substrate for liquid jet recording head 8 may be provided with a protective layer 4 for the purpose of protecting the wirings 3a, 3b and the heat generating resistor 2a. The protective layer 4 serves to prevent occurrence of electric corrosion or/and electric breakdown at the heat generating resistor 2a and the wirings 3a, 3b.
As the base member 1 of the substrate for liquid jet recording head 8, there can be mentioned plate-like members of silicon, glass, ceramics, or the like. However, in general, a single crystal silicon plate is used as the base member. The reason for this is due to the following situation. That is, in the case where a glass plate is used as the base member 1, there are disadvantages in that the glass plate is poor in thermal conductivity, and when the energization frequency (the drive pulse in other words) for the heat generating resistor 2a is increased, there is a fear that the heat generated by the heat generating resistor becomes excessively accumulated within the base member 1 and as a result, ink in the liquid jet recording head is heated by virtue of the heat accumulated to cause bubbles, resulting in providing defects in the ink discharging performance.
In the case where a ceramic plate is used as the base member 1, there are advantages such that the size of the substrate can be enlarged to a certain extent, and a ceramic plate having a larger thermal conductivity than that of the glass plate can be selectively used. However, even in the case of using such a ceramic plate, there are disadvantages such that the ceramic plate is usually accompanied by surface defects such as pinholes or minute protrusions of some microns to some tens microns in size because it is produced by baking powdery raw materials, and such surface defects are liable to short-circuit or disconnect the wirings, wherein a desirable production yield is hardly attained. There are further disadvantages in this case such that the ceramic plate is usually of a surface roughness of Ra (center line mean roughness)=about 0.15 .mu.m, and because of this, it is difficult to provide a surface roughness optimum for forming a desirable heat generating resistor layer 2 excelling in durability thereon; specifically in the case of preparing a liquid jet recording head using a plate made of alumina ceramics, because of the above reasons, a removal is often occurred between the base member 1 and the heat generating resistor layer 2 or a cavitation is often occurred at a part of the heat generating resistor layer formed on the defective surface of the base member when the bubbles generated are extinguished, resulting in disconnecting the heat generating resistor layer, wherein the performance of the heat generating resistor layer is eventually deteriorated.
In order to eliminate these problems in the case of using the ceramic base member 1, there is a proposal of polishing such roughened surface of the ceramic base member to smooth said surface whereby improving the adhesion between the base member 1 and the heat generating resistor layer 2 and preventing occurrence of the premature disconnection of the heat generating resistor layer which will be cased because of cavitations centralized at a part of the heat generating resistor layer. However, this proposal is poor in practicability since the alumina ceramics are of a high hardness and because of this, their surface roughness is hardly adjusted as desired.
Other than this proposal, there is another proposal in order to eliminate the above problems in that a glaze layer (a welded glassy component layer) is formed on the surface of such ceramic base member to thereby provide an alumina glaze base member. However, it is almost impossible to form the glaze layer at a thickness of less than a value of 40 to 50 .mu.m by the manner employable in the formation of a glaze layer. As well as in the case of using the glass base member, problems relating to occurrence of excessive accumulation of heat are liable to occur also in this case. Therefore, this proposal is also poor in practicability.
In the case of using a single crystal silicon plate as the base member 1, the above described problems relating to occurrence of excessive accumulation of heat are not occurred and the single crystal silicon wafer excels in surface property, and because of this, the foregoing problems relating to disconnection of the wirings and the like are not occurred. For this, for example, Japanese Unexamined Patent Publication No. 125741/1990 describes a substrate for the foregoing liquid jet recording head utilizing thermal energy, in which a single crystal silicon wafer is used.
Incidentally, in recent years, in the field of recording using the liquid jet recording method, there has been an increased societal demand for early provision of a recording apparatus capable of obtaining a high quality record image at an improved speed. In order to enable to conduct recording on a wide recording member in reply to such societal demand for high speed recording, various studies have been made of a large-sized recording head, i.e., a so-called full-line recording head having a widened discharging width corresponding to a large-sized recording member.
The results of the studies have revealed that the use a single crystal silicon wafer is optimum as the base member as long as the recording head to be prepared is of a relatively small size, but the use of a single crystal silicon wafer in the case of obtaining a large-sized recording head entails such problems as will be described below. Because of this, there are subjects necessary to be solved in order for the single crystal silicon wafer to be usable in a substrate for the large-sized recording head.
That is, in the case where a substrate for liquid jet recording head is prepared using a base member comprising a single crystal silicon material, the single crystal base member, i.e., a single crystal silicon wafer is usually obtained by quarrying a single crystal silicon ingot produced by the pull method. The single crystal ingot which can be presently produced by the pull method is a rod-like shaped one of 8 inches in diameter and about 1 m in length at the maximum. Therefore, there is eventually a limit for the size of a single crystal silicon wafer which can be quarried from the single crystal ingot. However, it is possible to quarry a single crystal silicon wafer having an enlarged size from the single crystal ingot. In this case, problems are, however, entailed in that the utilization efficiency is greatly reduced, resulting in unavoidably raising the cost of the resulting single crystal wafer, and this leads to raising the production cost of a final product.
In the substrate for liquid jet recording head, in order to facilitate thermal energy to transmit to the liquid recording medium, there is usually disposed, on the surface of the base member, a heat accumulating layer (a lower layer in other words) capable of attaining a desirable balance between the heat accumulating property and the heat radiating property. In this case, the substrate is obtained in a manner that a single crystal silicon wafer is obtained by quarrying the above described single crystal ingot, the surface of the single crystal silicon wafer obtained is subjected to thermal oxidation to form a SiO.sub.2 layer as the heat accumulating layer, the foregoing heat generating resistor layer and the foregoing wirings are successively formed, and the resultant is cut into a plurality of pieces each capable of serving as a substrate for liquid jet recording head.
In the viewpoint of obtaining a large-sized recording head, the present inventor examined these members obtained in the above manner. As a result, there was obtained a finding that some of them, which were quarried from the opposite end portions of the single crystal silicon wafer, are deformed in such a bow-shaped form as shown in FIG. 9(A). And their deformed magnitude (which will be hereinafter called "warp magnitude" or "warp degree") was found to be ranging in the range of 60 to 90 .mu.m. As for these deformed members, it was found that they are apt to break when their deformation is forcibly corrected. And as for some of the base members which are slight in deformation, it was found that there are still problems such that uniform polishing is sometimes hardly attained in the successive polishing step after the quarrying step, precise pattering sometimes cannot be conducted in the step of patterning wirings on the base member, and sometimes, it is difficult to precisely electrically connect the wirings arranged on the base member to an IC or the like.
It was also found that in the case where a liquid jet recording head should be obtained using such deformed base member, the liquid jet recording head unavoidably causes a positional deviation of a liquid recording medium to a recording member on which recording is to be performed due to the distortion of the base member, resulting in providing defects such as missing dots or/and uneven dots for an image recorded.
It is a matter of course that in the case where the end portions of the single crystal silicon wafer which are apt to cause the foregoing deformation are not used as a base member for a substrate for liquid jet recording head, the production cost for the substrate for liquid jet recording head unavoidably becomes very expensive.
The present inventor made studies of the reason why such work in process for a substrate for liquid jet recording head is deformed as above described. As a result, it was found that in the case of the work in process for a substrate for liquid jet recording head not having the foregoing thermal oxide layer as the heat accumulating layer on the base member, such deformation is hardly occurred, and thus, the occurrence of such deformation is due to the thermal oxidation process upon forming the foregoing heat accumulating layer. And there were obtained findings that since after the single crystal silicon wafer having been subjected to thermal oxidization, it is cooled wherein the end portions of the single crystal silicon wafer, particularly four corners thereof, are cooled for the first time, tensile stresses are caused at the periphery in a state as expressed by arrow marks in FIG. 8(A) and those stresses then become distributed into the inside in a state as expressed by (+) marks in FIG. 8(B); that when this single crystal silicon wafer is cut in order to obtain a substrate for liquid jet recording head, part of those stresses is released to make the substrate deformed in such a state as above described; and that when a film for the heat generating resistor and a film for the wirings are successively formed on such single crystal silicon base member, the resulting work in process becomes accompanied by a warpage for which desirable patterning cannot be performed because the focusing position upon exposure is deviated.
On the basis of the above findings, it was found that there is an inherent limit for the single crystal silicon wafer to be used as the base member for a substrate for liquid jet recording head in order to attain elongation of the substrate. Therefore, in order to obtain an elongated liquid jet recording head capable of attaining high speed recording, it is necessary to integrate a plurality of relatively short substrates for recording head. However, it is extremely difficult to adjust each of the joint portions among such substrates so that no negative influence is provided for an image recorded.
Thus, it is an earnest desire to provide an inexpensive substrate for liquid jet recording head which can be effectively produced without having any restriction for its form depending upon the production process and without occurrence of problems relating to deformation and the like and which enables to easily attain high speed recording.